Using morphometric traits for sexual determination in three species of Elaenia

Sexual identification is important for understanding several biological and evolutionary processes. For monomorphic species in plumage, this task is a challenge, especially during field expeditions. The application of Discriminant Function Analysis (DFA) using morphometric measures has been shown to be an important tool for bird sexing. In this work, we applied DFA using six morphometric measures (wing, tail, tarsus and bill lengths, bill height and width) for three species of Elaenia (Tyrannidae) without reported sexual dimorphism: E. cristata (EC), E. chiriquensis (ECH) and E. flavogaster (EF). The individuals were sampled in ornithological collections and field covering a latitudinal amplitude of 2,624 km (nEC = 58, nECH = 95 and nEF = 72; all samples were sexed using molecular techniques). Only morphometric measures that did not respond to longitudinal variation were analyzed. Our analysis was able to accurately predict the sex of 72% of EF individuals, 74% of ECH individuals and only 60% of EC individuals according to jackknife tests. The width, length and height of the bill and the length of the tarsus were the morphological variables that provided the best rates for sex discrimination of EF. For ECH, wing and tail lengths provided the best rate for sex identification. DFA analysis has proved to be a reasonably useful tool for sexing E. chiriquensis and E. flavogaster, species apparently monomorphic, with important implications for field studies.